User:Jstapko/EngLab/PrinterVoltmeter

Printer Based Recording Voltmeter

Problem
HCC's lab has stacks of computer power supplies in various states decay. Some reportedly have intermittent problems. The goal of this project is to build a device that can monitor and record voltages at several points within power supplies simultaneously. The intent is that when the intermittent fault occurs, some voltages will change and some will remain the same, and the recorded charts of voltages can be used to pinpoint what parts of the circuit stop working during the fault. This should then assist greatly in finding the cause of the fault so that the power supply can be fixed.

Solutions

 * 1) Hospitalier Ondograph
 * 2) multi channel oscilloscope with video camera (suggested on Repair FAQ: Troubleshooting And Repair of Consumer Electronics Equipment
 * 3) Digelent Explorer board with suitable connections (suggested by Professor Foerster)
 * 4) Converted InkJet Printer (scope of this page)

Conceive
An arduino will be interfaced to an ink jet printer and suitable accessory electronics in such a way that the arduino will cause the printer to print a line on the paper that mirrors a voltage fed to an analog input pin of the arduino.

Reverse Engineering
1) salvaged a printer While cleaning the storage room CL-160, I found a computer power supply labeled "works intermittently" or wording with similar meaning. I was thinking of ways that I might be able to monitor the output voltage over a long period of time, and look for patterns or make measurements at those times that there was no output.  I had recently been browsing through my collection of Hawkins Electrical Guides, and remembering those, thought to myself "If only I had a, I could hook the ondograph to the PSU's output and record the voltage over time.  Not having one, I started thinking in terms of something functionally equivalent, such as a computer controlling the position of a motor (this is technology available in the lab) which drives a linear actuator, which holds a pen that draws a line on paper.  Another option I considered was voltmeters, oscilloscopes, or both on the different test points, and a video camera with counter recording all the instrument's outputs. Then the status of all the instruments could be checked simultaneously at any particular instant. Other options considered at the time were Processing, to be used with the Arduino, or the Digilent Explorer boards (the last 2 options were suggested by Mr. Foerster.

More urgent projects pushed the power supply troubleshooting problem to a low priority, but it was revived when I was dismantling a printer to get magnets for the magnetic drill bit holder project. The thinking was that there would be permanent magnet motors in the printer from which magnets could be salvaged. This was not the case, but while staring at the disassembled carriage complete with motor drive pulley, ink dispensing system, and position sensor, I thought it should be fairly simple to tap into the sensing and actuating circuitry and drive them with an arduino, so that the horizontal position of the carriage would correlate to the voltage of the power supply, and a motor would simply turn and move paper through the printer, while the ink cartridge marked a line showing the input voltage, a 21st century version of the Hospitalier Ondograph. Thus were the conditions from which arose the project hereinafter described.

Subsystems

 * 1) Arduino
 * 2) Voltage divider to reduce the voltage from the power supply under test to a value safe for the arduino
 * 3) Linear optical encoder strip and quadrature encoder sensor to tell the arduino the ink carriage's position
 * 4) Motor drive amplifiers to connect the arduino to the ink carriage motor and paper feed motor
 * 5) Power supplies for the arduino and motor drive amplifiers
 * 6) cables for connecting arduino, drive amplifiers, motors, and sensors
 * 7) Code to allow the arduino to :
 * determine where the ink carriage should be, based on the voltage of the power supply under test
 * determine where the ink carriage is, based on the readings of the quadrature encoder
 * send commands to the motor to move the carriage toward the position it should be in
 * send commands to the paper drive motor to feed paper very slowly
 * send commands to the print heads to print a line showing the output voltage

(t may be possible to represent several different input voltages with lines of different colors or line patters if the ink carriage can move very fast compared to the paper speed, or even feed the paper backwards and print several complete lines, if the carriage and paper feed motors are fast compared to the sample rate)

Problems

 * 1) Inkjet cartridge reverse engineering
 * 2) Arduino
 * 3) Motor Drive amplifier for arduino to drive the ink carriage motor(former RC car power board
 * 4) Power supply for the ink carriage motor drive amplifier
 * 5) Cable to connect the ink carriage motor to the motor amplifier
 * 6) Cable to connect the ink carriage motor drive amp to the arduino
 * 7) Optical encoder I/O pin determination and voltages
 * 8) Cable to connect the optical encoder to the arduino inputs
 * 9) motor drive amplifier and associated interconnecting cables to allow the arduino to run the paper drive motor

Next Steps

 * upload pictures of work done on this project
 * describe in detail work already done on this project
 * upload links to information found to be useful while working on this project
 * create separate pages for individual subsystems, and spinoff projects such as the helipot repair effort
 * describe the current problems more carefully
 * look into the alternative solutions, such as processing or the Digilent boards more thoroughly, particularly because they might be paperless, thus reducing environmental impact.